Microwave transducer and electron device with microwave transducer



March l1, 1969 YOS|||H|5A SUZUKl ET AL 3,432,716

MICROWAVE TRANSDUCER AND ELECTRON DEVICE WITH MICROWAVE TRANSDUGER Sheet Filed Feb. 13, 1964 NVENTOR. YOSMMSLL Suzuki Yosluo Tqngkq Wt 5km mlshrw March 1l, 1969 YOSHIHISA SUZUKI ET Al- MICROWAVE TRANSDUCER AND ELECTRON DEVICE WITH MICROWAVE TRANSDUCER Filed Feb. 13, 1964 sheet 2 ora Fl fl MICROWAVE TRANSDUCER INVENTOR. Yusnksa Sau... ld BY YOSMO Ttntkt United States Patent O 3,432,716 MICROWAVE TRANSDUCER AND ELECTRON DEVICE WITH MICROWAVE TRANSDUCER Yoshihisa Suzuki, Tokyo-to, and Yoshio Tanaka, Musashino-shi, Japan, assignors to Kabushiki Kaisha Hitachi Seisakusho, Chiyoda-ku, Tokyo-to, Japan, a joint-stock company of Japan Filed Feb. 13, 1964, Ser. No. 344,768 U.S. Cl. S-3.5 5 Claims Int. ICl. H01j 25/34 ABSTRACT OF THE DISCLOSURE A microwave transducerconstructed so that an aperture for leading a parallel two-wire line into a rectangular waveguide is provided on the side wall of the waveguide, a loop is formed at the extreme end of the parallel twowire lines thus led in, or pipes are itted at the top and bottom walls of the waveguide, through which the parallel two-wire line passes, each wire being bent in mutually opposite directions, thereby coupling the waveguide and the wire lines in a high-frequency manner.

This invention relates to the transmission device of high frequency signals such as microwaves, and more particularly it relates to a new microwave transducer for coupling for radio frequency a parallel two-Wire line, which is a -balanced transmission line, and a waveguide. The invention also relates to a biiilar helix backward wave tube provided with the said microwave transducer.

AS is well known, for propagating high frequency signals such as microwaves, in general, transmission lines of different types such as parallel two-wire lines, coaxial cables, and waveguides are utilized as the frequency of the signal to be transmitted increases, the type of transmission line which is most suitable for the signal to be transmitted being used. 'Ihis does not mean, however, that between the various types of transmission lines used, there are distinct boundaries in terms of frequency regions. That is, two types of transmission lines are utilized in some cases, and various types of transducers which are intended for radio-frequency coupling of a parallel twowire line and a coaxial cable or a coaxial cable and a waveguide have heretofore been proposed. However, to the best of the present inventors knowledge, the direct and perfect (lossless) coupling for radio frequency of a parallel two-wire line and a waveguide has never been used in practice.

The first object of the present invention is to provide a transducer capable of accomplishing the abovesaid direct radio-frequency coupling of a parallel two-wire line and a rectangular waveguide.

The second object of the invention, in another aspect thereof, is to provide a coupling part for coupling a bifilar helix backward wave tube and an input circuit or an output circuit.

The foregoing objects, as well as other objects and advantages as will presently become apparent, have been achieved by the present invention, the speciic nature and details of which will be most fully understood by reference to the following description, taken in conjunction with the accompanying drawing in which like parts are designated by like reference characters, and in which:

FIGURE l is ,a fragmentary perspective view, with ICC parts cut away, diagrammatically showing a preferred embodiment of the transducer according to the invention;

FIGURE 2 is an elevational sectional view diagrammatically showing another embodiment of the transducer according to the invention;

FIGURE 3 is an elevational view, in vertical section with a part cut off, showing the construction of one example of an electron device wherein the transducer shown in FIGURE 2 is used; and

FIGURE 4 is an enlarged schematic diagram indicating the arrangement of an essential part of the device shown in FIGURE 3.

In the embodiment of the transducer of the invention shown in FIGURE 1, as waveguide 1 and a parallel twowire line (2, 2a) are coupled according to the invention. The line (2, 2a) is led into the waveguide 1 through a lead-in aperture 3 which is provided on a side wall of the waveguide and has an inside diameter corresponding to approximately 3 times the distance between the wires of the parallel two-wire line. The ends of the wires of the parallel two-wire line are led in through the aperture 3 and then bent in mutually opposite directions to form loops 4 and 4a in mutually opposite directions. As a modification, it is possible to form equivalent loops also by electrically connecting the respective ends 5 and 5a of the two wires forming the loops to oppositely disposed positions `6 and 6a respectively on the upper and lower walls of the waveguide. By forming a tapered or funnelshaped part 7 on the outer end of the aperture 3 as shown in FIGURE 1, it is possible to afford excellent matching.

According to the transducer of the above description, since the loops 4 and 4a are in mutually opposite directions wit-h respect to the magnetic flux within the waveguide, balanced modes having mutually opposite currents are generated at the parallel two-wire part, whereby radiofrequency coupling of the parallel two-wire line and the waveguide is attained.

It has been found as a result of a simple experiment with a device as above described that radio-frequency power can be transmitted Iwith a coupling loss of the order of 0.5 db.

In the case when the parallel two-wire line and the waveguide are to be dielectrically isolated, tubes 8 and 8a, each having a length equal to 1A wavelength, are connected as shown in FIGURE 2 to the waveguide at its parts on its upper and lower walls in line with the parallel two wires, and the wires of the parallel two-wire line are respectively passed centrally through these tubes 8 and 8a in a state dielectrically isolated therefrom. By such an arrangement, a coaxial choke is formed, whereby a radiofrequency coupling similar to that described hereinabove in conjunction with FIGURE 1 is obtainable.

Ordinarily, a waveguide is used for wavelengths of the centimeter wave region or shorter, and parallel two-wire lines are not ordinarily intended to be utilized for such short wavelengths, but in the case of very short distances as in the case of an input or output transducer of elec- ,tronic tubes, it is sometimes more suitable to use a balanced transmission line in the form of a parallel twowire line. The present invention proposes the most suitable device as a device to be used in such cases as described above.

In another aspect of the present invention as mentioned hereinbefore, it is contemplated to provide a coupling part for coupling biiilar helix backward wave tubes and an input circuit or an output circuit.

It is known in the art that, in general, by using a bifilar helix for the delay line of a traveling wave tube or a backward wave tube, it is possible to obtain excellent characteristics with high beam coupling impedance. That is, there are two forms of the wave propagated in the case wherein a biilar helix is used. One is of the same waveform as in the case of a single helix, and the other is similar to the waveform obtained when a parallel twowire pair is helically wound. These two forms will herein be referred to as o mode and 1r mode, respectively. Since the beam coupling impedance with respect to the 1r mode is higher, a 1r mode oscillation is obtained in the case wherein a bitilar helix is used in a backward wave tube. However, the coupling method for extracting the output of such an arrangement has, heretofore, never been proposed. As methods of coupling o mode, there are such methods as the method utilizing a coupled helix, the method of antenna coupling, and the coaxial line coupling method but none of these methods are fully satisfactory in the case of the 1r mode. By a common practice, the transduced part in the o mode of the output is extracted by means of a mode coupling device in spite of the fact that operation of a bitilar helix backward wave tube conforms to the 1r mode, but by this method, only about $50 of the power output of the oscillator can be extracted.

The present invention, which affords a method of fully extracting the 1r lmode output of a bilar helix backward wave tube, is based on the observation that the 1r mode operation is similar to that of the form of the electromagnetic wave in the case wherein a parallel two-wire line is helically wound and affords a method and means of extracting output from a bilar helix into a parallel two-wire line.

Heretofore, it has been considered that frequencies for which parallel two-wire lines can be utilized are up to the order of a number of hundreds of megacycles. For this reason, the use of parallel two-wire lines as transmission lines for the microwave region and the millimeter wave region, for which backward wave tubes are used, has not been considered. It has been found, however, that it is possible to utilize such parallel two-wire lines, without any difficulty whatsoever, in applicatons to short distances, such as that of the input or output part of a backward wave tube. Results of experiments indicate that the loss at such a part is 0.1 db or less. Although, in such cases, it is difficult to couple the output of the parallel two-wire line further to an ordinary waveguide, it has become possible for the first time to overcome this diiculty by using the microwave transducer according to the invention described hereinbefore. Moreover, by the use of the said transducer, it has become possible to reduce the losses at the aforesaid input and output parts to innitestimal values.

In one embodiment of the biilar helix backward Wave tube so designed according to the invention as shown in FIGURE 3, there are provided a cathode 11, a beam forming electrode 12, a rst anode 13, a second anode 14, a bilar helix as shown in enlarged view in FIG- URE 4, a coupling part 16 for coupling the said -biflar helix 15 by way of a parallel pair of wires 17 to a waveguide 18, the said coupling part being, for example, the microwave transducer according to the invention as illustrated in FIGURE 1, a vacuum-tight, radio-frequency output window 19, a collector 20, and a vacuum-tight envelope 21.

In the operation of the bililar helix backward wave tube of the above described construction, the radio frequency energy produced by the biilar helix 15 which effects interaction while the electron beam emitted and directed from the cathode 11 is caught in the collector 20 is transmitted by way of the parallel pair of wires 17 and the microwave transducer 16 to the waveguide 18 and is extracted out through the vacuum-tight window 19. Thus, in such a constructional arrangement, the microwave transducer as described in detail hereinbefore is of great importance. The details of the aforesaid coupling part which the present invention has rendered capable of coupling the bililar helix and the waveguide will be more fully apparent from the following description with reference to FIGURE 4 which shows its essential parts.

These essential parts are a bilar helix 15, a parallel two-wire line 17, Ia microwave transducer 16 for supplying the output power on the parallel line to the waveguide, and a shield case 22. When an electron beam is passed through the interior of the biflar helix 15, a radiofrequency electromagnetic wave is induced in the biilar helix. This operation is well known as the operation of a backward wave tube. Since the electromagnetic wave so induced is a 1r mode electromagnetic wave similar to that produced in the case wherein a parallel two-wire line is helically wound, it is possible to extract radio-frequency power output with high efliciency by connecting the parallel two-wire line 17 directly to the end of the bililar helix 15 as shown in FIGURE 4.

In order to prevent leakage of the radio-frequency electromagnetic wave to the outside and, moreover, to shield out effects from the outside, a shield case 22 can be used. Furthermore, since by varying the thickness of this shield, the radio-frequency impedance can be varied, this shield can be utilized for impedance matching of the bilar helix section and the parallel two-wire section.

While the above description has concerned the output coupling part which is an essential part of the biiilar helix backward wave tube according to the invention, it is possible, of course, to use this coupling part also for the input circuit of the said bitlar helix backward tube. Thus, by the practice of the present invention, it is possible to obtain a highly efficient coupling part with excellent frequency characteristics for the coupling of a bitilar helix backward wave tube and the input or output circuit therefor.

=It should be understood, of course that the foregoing disclosure relates to only preferred embdirnents of the invention and that it is intended to cover al1 changes and modifications of the examples herein chosen for the purposes of the disclosure, which do not constitute departures from the spirit and scope of the invention as set forth in the appended claims.

What is claimed is:

1. A microwave transducer comprising a TEM mode rectangular waveguide provided with one lead-in aperture on its sidewall; a parallel two-wire line being led into said waveguide through said aperture, the diameter of said aperture being at least three times the distance between the two parallel wires, the end part of each wire being bent in mutually opposite direction and butt-connected to a part of the wall of said waveguide, forming a coupling loop therewith.

2. The transducer as defined in claim 1, wherein cach wire is butt-connected to the respective upper and lower part of said waveguide.

3. The transducer as defined in claim 1, wherein each wire is butt-connected to the side Wall of said waveguide.

4. A high-frequency electron device comprising a bilar helix slow-wave structure and at least one microwave transducer according to claim 1; said structure being so arranged as to interact with an electron beam of said device and said transducer; said two-wire line being led to said bilar helix, thereby coupling the electron device with said waveguide.

5. A microwave transducer comprising: a rectangular waveguide provided with one lead-in aperture in one sidewall thereof; -a parallel two-wire line led into said waveguide through said aperture; and two coaxial chokes, each having an outer and an inner conductor, the lead-in end part of each wire being bent in mutually opposite direction and connected with said coaxial chokes, respectively, said outer conductors being connected to the upper and lower wall of the waveguide, respectively, and said inner conductors being insulatively coupled to said outer conductors, but short circuitedly coupled thereto at a high `frequency, said inner conductors being the respective end parts of said wires.

References Cited UNITED STATES PATENTS 2,142,159 1/1939 Southworth et a1. 329-161 2,834,909 5/1958 Beaver 'S15-3.6 2,859,375 11/1958 Brewer S15-3.6

2,437,244 3/ 1948 Dallenback 333-26 3,239,713 3/1966 Evan et al. 333-26 X 3,280,362 10/1966 Ohtomo 315-3.6

FOREIGN PATENTS 1,130,197 9/1956 France.

HERMAN KARL SAALBACH, Primary Examiner.

SAXFIELD CHATMON, JR., Assistant Examiner.

U.S. Cl. X.R. 

